Not applicable.
The properties of liquefied petroleum (LP) gases and other hazardous materials are described in the standard of the National Fire Protection Association (NFPA) as products which are gases at normal room temperature and atmospheric pressure. They liquefy under moderate pressure, readily vaporizing upon release of the pressure. The potential fire hazard of LP-Gas vapor is comparable to that of natural or manufactured gas and their ranges of flammability are considerably narrower and lower. For example, the lower flammable limits of the more commonly used LP-Gases are 2.15% for propane and 1.55% for butane, those values representing volumetric percentages of gas in gas-air mixtures. See: ANSI/NFPA 58.
The commercial distribution of these liquefied gases from major production facilities, particularly in the case of propane, involves the utilization of stationary distribution installations or xe2x80x9cplantsxe2x80x9d which may serve a single industrial complex or a wide range of smaller customers located within a practical product transportation range, for instance, about forty miles. Typically, transport from the production facilities to the distribution plant is by semi-truck implemented transporters having about a 10,000 gallon tank capacity.
The layouts of the distribution facilities vary considerably depending upon the needs of the locally served market. Such distribution facilities generally are climatically open fenced-in regions within which one or several steel stationary tanks, typically having a capacity of 30,000 gallons or 18,000 gallons, are supported upon concrete cradles. Those cradles are designed to accommodate for temperature induced tank contraction and expansion. These steel tanks are fabricated under American Society of Mechanical Engineers (ASME) published specifications. The noted larger capacity transporter vehicles periodically off-load the hazardous liquid product into these tanks utilizing a somewhat well established procedure. In this regard, spaced about five to ten feet from the tanks are one to several concrete or steel supported stanchions supporting conduits, valves and the like extending to the stationary tank through which product is pumped from the transporter. Such valves include a fire valve located at the bottom of the tank communicating with its liquid region and having a fuzable link which releases a spring valve closure mechanism at temperatures above 212xc2x0 F. Also incorporated within the system are excess flow valves designed to close when the liquid passing through them exceeds the prescribed flow rate as determined by pressure drop. These valves assume an open state upon fluid delivery into the stationary tanks and will close in the event product is inadvertently released. The fire valves may be opened manually, or by using explosion-proof solenoid actuators or, more typically, utilizing a pneumatic system which, when pressured with gaseous nitrogen, causes the valve to open and to close automatically under spring bias with loss of such pressure. Piping extends from these valves to flow control valving adjacent the stanchions which, in turn, are connected in fluid transfer relationship with the trailer born transporter tanks. During a loading procedure, vapor equalization conduits are coupled to extend between the vapor regions of the stationary tank and the transporter tank.
The most prevalent off-loading from the stationary tank is into smaller distribution trucks having frame-mounted smaller tanks. Such delivery vehicles are referred to as xe2x80x9cbobtailsxe2x80x9d. To carry out the product loading of a bobtail, the vehicle is parked adjacent to a stanchion. A pneumatically enabled emergency shut-off valve (ESV) is mounted at the stanchions which is in fluid communication with an electric motor driven pump which, in turn, is coupled in fluid transfer relationship with one of the above-noted fire valves. Upon coupling the bobtail tank with the stationary tank at the stanchion, the motor activated pump is energized and the ESV valve is opened. The ESV valve will remain open as long as pneumatic pressure is present. However, with the loss of such pressure, the valve is spring biased to close. In general, the explosion proof pump motors are energized from induction starters located quite remotely from the stationary tanks. Accordingly, it is necessary for the fire valves to be opened and the motors enabled as well as the pneumatic system as part of the procedure for loading the bobtails. While some of the distribution facilities will be quite elaborate, incorporating satellite loading components for filling variety of steel containers ranging from small portable cylinders to skid mounted larger tanks, in many instances the plants are unattended, accidents must be anticipated. Where dangerous incidences do occur, then it is appropriate for personnel to exit the region forthwith, a proper procedure, but one which may leave the distribution facility in a perilous condition. Many of these distribution facilities are substantially un-manned. As a consequence the bobtail driver or transport operator must open and activate the facility as well as close and de-activate it. For instance the bobtail driver is called upon to activate the pneumatic system to open an appropriate fire valve, energize an appropriate pump motor through the remote starters and then reverse the procedure upon completion of filling, whereupon the bobtail exits the plant. Calling upon the delivery truck drivers to carry out these procedures is not considered desirable and, accordingly, many truck mounted safety features have been mandated by regulatory authorities.
The present invention is addressed to a system and method for controlling a distribution facility for hazardous including combustible fluids such as propane. With the system, an operator, upon entering the facility, prepares it for either filling a distribution tank or supplying the facility with fluid by actuating a housing mounted power switch from an off to an on condition. Then the operator depresses a start of reset switch for an interval sufficient to pressurize the pneumatic system of the facility, typically an interval amounting to about 1 to 15 seconds. The facility then is ready for the carrying out of distribution tank filling or storage tank supply procedures. At the completion of such a distribution or supply activity, the operator, upon disconnecting from the facility, simply returns to the remotely disposed housing and activates the power switch from its on-state to its off-state. This causes the complete shut-down of the system including the closing of tank valves, removal of enabling pneumatic pressures from emergency shut-off valves, and the disenablement of electric pump components.
As another feature of the invention, the control system incorporates a receiver at the noted housing which responds to emergency shut-off transmission broadcast from strategically positioned transmitters. In the event of a perceived emergency, personnel, upon rapidly leaving the facility will encounter simply activated shut-down switches which cause the transmitter to broadcast to the receiver causing the carrying out of the noted shut-down procedure automatically. The receiving circuit additionally polls the emergency transmitters to determine their operational status. In the event of a defective transmitter, a perceptible cue is energized and the defective transmitter is identified for correction.
The invention further features a method for controlling a hazardous fluid distribution facility having a perimeter with an entrance, an electrical power input, a source gas under pressure, a principal fluid storage tank, a tank valve pneumatically actuable to provide fluid flow communication with the principal storage tank and having a closed state in the absence of such actuation, a fluid pump in fluid flow communication with the tank valve, a motor coupled to drive the fluid pump when enabled and actuated, a fluid transfer station and a fill valve in fluid flow communication with the pump and connectible when pneumatically enabled and actuated in fluid delivery communication with a distribution tank, the fill valve having a closed state when pneumatically disenabled, comprising the steps of:
providing a power switch coupled with the electrical power input, the power switch being actuable to provide an electrical power output and an off condition;
providing a start switch coupled with the power switch and actuable to respond to the electrical power output to provide an on-state input;
providing an electrically controllable valve coupled in gas flow relationship between the source of gas under pressure and a gas conduit assembly extending to the tank valve and the fill valve, responsive to an on-state input to convey gas under pressure from the source into the gas conduit assembly and effecting a venting of the gas conduit assembly in the absence of the on-state input;
providing a gas pressure monitor responsive, when enabled, to the pressure of gas at the conduit assembly, having a system enable condition when the gas pressure is at an enable value and having an off condition when the gas pressure is lower than the enable value;
actuating the power switch to provide an electrical power output;
actuating the start switch to derive the on-state input and to enable the gas pressure monitor for an interval sufficient to derive the system enable condition effecting the pneumatic actuation of the tank valve and enablement of the fill valve and the motor;
actuating the motor and the fill valve and delivering fluid from the principal storage tank to the distribution tank; and
then actuating the power switch to provide the off condition to effect the venting of the gas conduit assembly at the electrically controllable valve to in turn, effect the closed state at the tank valve, effect the disenablement of the fill valve, and effect disenablement of the gas pressure monitor and the motor.
As another feature, the invention provides a method for controlling a hazardous fluid distribution facility having a perimeter with an entrance, an electrical power input, a source of gas under pressure, a principal storage tank, a fluid tank valve pneumatically actuable to provide fluid flow communication with the principal tank and having a closed state preventing the fluid flow communication in the absence of the pneumatic actuation, a vapor tank valve pneumatically actuable to provide vapor communication with the principal storage tank and having a closed state preventing the vapor communication in the absence of the pneumatic actuation, a fluid shut-off valve actuable when pneumatically enabled to provide fluid flow communication with the principal storage tank through the fluid tank valve and having a closed state when pneumatically disenabled, a vapor shut-off valve actuable when pneumatically enabled to provide vapor communication with the principal storage tank through the vapor tank valve and having a closed state when pneumatically disenabled, a fluid transfer station adjacent the fluid shut-off valve and the vapor shut-off valve for receiving the combustible fluid from the pumped fluid output of the supply tank of a delivery vehicle located adjacent the fluid transfer station, the vehicle supply tank having a vent input, comprising the steps of:
providing a power switch in electrical communication with the electrical power input, the power switch being actuable to provide an electrical power output and an off condition;
providing a start switch in electrical communication with the power switch and actuable to respond to the electrical power output to provide a system start output;
providing an electrically controllable valve coupled in gas flow relationship between the source of gas under pressure and a gas conduit assembly extending to the fluid tank valve, the vapor tank valve, the fluid shut-off valve and the vapor shut-off valve, responsive to an on-state input to convey gas under pressure from the source into the gas conduit assembly and effecting a venting of the gas conduit assembly in the absence of the on-state input;
providing a gas pressure monitor responsive when enabled to the pressure of the gas at the conduit assembly, having a system enable condition when the gas pressure is at an enable value and having an off condition when the gas pressure is lower than the enable value;
actuating the power switch to provide the electrical power output;
actuating the start switch to derive the on-state output and to enable the gas pressure monitor for an interval sufficient to derive the system enable condition effecting the pneumatic actuation of the fluid tank valve and the vapor tank valve, and the enablement of the fluid shut-off valve and the vapor shut-off valve;
coupling the delivery vehicle supply tank pumped fluid output in fluid transfer relationship with the fluid shut-off valve;
coupling the delivery vehicle supply tank vent input with the vapor tank valve;
actuating the enabled fluid shut-off valve and the enabled vapor shut-off valve;
providing combustible fluid from the supply tank to the principal storage tank;
actuating the power switch to provide the off condition to effect the venting of the gas conduit assembly at the electrically controllable valve to, in turn, derive the closed state at the fluid tank valve and the vapor tank valve and to pneumatically disenable the fluid shut-off valve and the vapor shut-off valve;
decoupling the delivery vehicle supply tank pumped fluid output from the fluid shut-off valve; and
decoupling the delivery vehicle supply tank vent input from the motor shut-off valve.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter. The invention, accordingly, comprises the method and system possessing the construction, combination of elements, arrangement of parts, and steps which are exemplified in the following detailed description.
For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in connection with the accompanying drawings.